Prior art injection valve assemblies generally include a nozzle which is operatively connected to a mold and means for injecting resin material into the mold. Usually a hydraulic cylinder controls an axially displaceable pin disposed within the main channel of the nozzle. The pin opens and closes the channel to control the flow of the resin material therethrough. In order to purge the system for a different material or for a shutdown of the assembly, the mold is spread open and the system is externally purged by running solvent through the assembly and out of the nozzle. This purging operation is quite sloppy and, accordingly, grossly inefficient. An example of such a device is shown in the U.S. Pat. No. Re. 28,721 to Farrell. The Farrell patent teaches an injection nozzle assembly including a valve having a first position which allows flow of material between a first and second passageway. The valve further has a second position which closes off the passage of material between the passageways. However, the Farrell patent does not teach an injection nozzle assembly including a valve for controlling internal purging of the injection nozzle or for controlling post-purge flushing of the system.
The U.S. Pat. No. 2,551,439 to Kovacs and U.S. Pat. No. 4,260,348 to Graham are also pertinent in regard to the instant invention. Kovacs and Graham both disclose injection nozzles including internal coolant circulation channels. However, neither of the two above-cited patents disclose an internal coolant circulation channel which bifurcates about the portion of the assembly nearest to the mold, the bifurcation providing the greatest amount of cooling capacity at the portion of the assembly which is exposed to the greatest heat.